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SHROPSHIRE: The movement of an exoplanet twice the size of Earth and eight times the mass has been detected only 41 light years away from us using data from NASA's Spitzer satellite.

Located in the Cancer constellation, this planet has been classified a 'super-Earth' because it has a mass greater than the Earth's but less than that of the Solar System's gas giants.

Due to discrepancies between results from the Spitzer team's study and a separate, simultaneous study of the planet, researchers have suggested that this could indicate the presence of an atmosphere.

"We can say that now for the first time we have a solid exoplanet that we can study in detail," said co-author Michaël Gillon from the University of Liège in Belgium of the paper published in Astronomy & Astrophysics. "We already know that it is very different from the planets of our own Solar System."

Exotic super-Earth

Look up into the sky on a dark, clear night and you may be able to spot this planet's host star, 55 Cancri (55 Cnc). This binary star consists of a yellow dwarf star, like our Sun, and a smaller red dwarf star.

Five planets orbit around 55 Cnc, making it one of the largest known planetary systems outside the Solar System. The super-Earth described in this study, named '55 Cnc e', is the innermost of these planets, and first discovered in 2004.

"We could call this planet a 'naked Neptune', as it is very similar to Neptune except that it has no gaseous envelope of hydrogen above its ice shell", said co-author Brice-Olivier Demory from the Massachusets Institute of Technology (MIT).

Although super-Earths are not uncommon - the Kepler space observatory mission recently released a list of around 300 new super-Earth candidates - 55 Cnc e is of special interest to astronomers because it is unusually small and dense, and the strong brightness of its host star makes sensitive measurements possible.

Catching shadows

The results of the new study were obtained by monitoring the transit of 55 Cnc e across its star, a method commonly used to detect exoplanets. When the planet crossed 55 Cnc, the observed brightness of the star dropped by a tiny amount, the dimming detected by the sensitive Spitzer space telescope.

The planet's radius was then determined by studying the resulting 'light curve'. Combining this with measurements of the planetary mass led to an estimated average density of around 4.5 g/cm3 for 55 Cnc e.

This result indicates a solid, rocky-iron core, similar to the Earth's. However, surface conditions are far from Earth-like: this planet is so close to its star that a year lasts 18 hours, and surface temperatures may reach an inferno-like 2,700 degrees Celsius.

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